Most handheld computers are equipped with limited memory resources. Usually, the memory resources are split into three sections: (1) ROM used to bootstrap the handheld computer when power is turned-on and contains the operating system (OS) and programs which provide access to low-level applications; (2) random access memory (RAM) used as an execution area for the computer's processor(s); and RAM used as file system storage.
Programs stored in ROM were originally permanently “burned-in” and could only be replaced by physically replacing the ROM medium. Now, with the advent of configurable non-volatile memory devices, such as flash memory devices, it is possible to update the contents of a ROM without physically replacing the ROM medium.
There are generally two common techniques used to update the contents of a flash ROM in handheld computers. The first technique is commonly referred to in the industry as “shadowing,” which involves storing updateable components of the ROM in the RAM file system area. The handheld computer then accesses the updated components from the RAM file system rather than the prior version of the component originally stored in ROM. There are, however, several problems with shadowing. Updated components consume valuable RAM space. Some updates in fact, are often tool large to fit in the RAM file system. Additionally, if the handheld computer is ever cold booted (in which the RAM is cleared) then the updates will be permanently lost.
Another technique used to update the contents of a ROM involves re-flashing the entire ROM image using the boot loader. The boot loader or “bootstrap” is used to initially instruct the handheld computer to load certain components in the ROM when the handheld computer is cold or warm booted. A drawback with this technique is that most handheld computers have limited memory and are unable to store the entire new version of the ROM image while performing the re-flash. So, in most situations, the entire updated ROM image must be staged on a companion host computer and fed to the handheld device via an interconnect, such as a serial or USB interconnect.
In any event, many of the components stored in ROM are manufactured and owned by different entities. This creates a dilemma when it is necessary to modify a component of the ROM, which requires modifying the entire ROM image; including components potentially not owned by the party that desires to release the updated component. So when one entity desires to modify its component to the ROM, it may not be possible to obtain access or permission to copy the rest of the ROM components owned by one or more third party entities.